build_abi.sh: add documentation for ABI_DEFINITION env variable
That has been heavily used for quite a time. Just figured it could need
some explanation here.
Change-Id: I78fcb74a949a3606d3c1f93a36e2d584b0eb3fbb
Signed-off-by: Matthias Maennich <maennich@google.com>
diff --git a/build_abi.sh b/build_abi.sh
index 7df69fa..c0ebea3 100755
--- a/build_abi.sh
+++ b/build_abi.sh
@@ -22,6 +22,14 @@
# ABI_OUT_TAG
# Customize the output file name for the abi dump. If undefined, the tag is
# derived from `git describe`.
+#
+# ABI_DEFINITION
+# Specify an expected Kernel ABI representation. If defined, this script
+# will, in addition to extracting the ABI representation from the currently
+# built kernel, compare the extracted ABI to the expected one. In case of
+# any significant differences, it will exit with the return code of
+# diff_abi and optionally (-r) print a report.
+# ABI_DEFINITION is supposed to be defined relative to $KERNEL_DIR/
export ROOT_DIR=$(readlink -f $(dirname $0)/..)
